1. Field of the Invention
The present invention relates to a liquid crystal display device used for a monitor of, for example, computers, wordprocessors, car navigation systems, and TVs, and a method for producing the same.
2. Description of the Related Art
Today, TN (twisted nematic) liquid crystal display devices (hereinafter, referred to as xe2x80x9cLCD devicesxe2x80x9d) are in wide use. In a TN LCD device, upper and lower alignment layers are treated by rubbing in different directions from each other, so that liquid crystal molecules are in a twisted alignment in the state where no voltage is applied. The TN LCD device has problems of a gray scale inversion phenomenon and an excessive dependency of the display quality on the viewing angle.
In order to solve such problems, a liquid crystal material having a negative dielectric anisotropy and a vertical alignment mode which uses a vertical alignment layer has been proposed. The vertical alignment mode provides a black display when no voltage is applied. A satisfactory black display is obtained in a quite large viewing angle range by using, for example, a phase plate having a negative refractive index anisotropy. The use of such a phase plate substantially compensates for birefringence caused by a liquid crystal layer in which the liquid crystal molecules are vertically aligned when no voltage is applied. In this manner, a high contrast display is realized in a wide viewing angle range. However, the vertical alignment mode has the problem of a gray scale inversion phenomenon which is observed in a direction identical with the direction in which the liquid crystal molecules are tilted when a voltage is applied.
Japanese Laid-Open Publication No. 6-301036 discloses an LCD device having an opening at a center of an area of a counter electrode, the area corresponding to a pixel electrode. Such a structure causes an electric field between the pixel electrode and the counter electrode to be inclined with respect to surfaces thereof, whereas the electric field is vertical with respect to the surfaces without such a structure. Accordingly, when a voltage is applied in the vertical alignment mode, the liquid crystal molecules are tilted in an axially symmetrical manner. The dependency of the display quality on the viewing angle of such an LCD device is averaged in all azimuth directions when compared with an LCD device in which the liquid crystal molecules are tilted in one direction. As a result, the LCD device disclosed in the above-mentioned publication provides a quite satisfactory viewing angle characteristic.
Japanese Laid-Open Publication No. 8-341590 discloses an LCD device having a projection surrounding a pixel region or divided pixel region and also an alignment fixing layer. Such a structure defines the position and the size of the liquid crystal region in which the liquid crystal molecules are aligned in an axially symmetrical manner, and stabilizes the axially symmetric alignment of the liquid crystal molecules.
However, the structure disclosed in Japanese Laid-Open Publication No. 6-301036 makes it difficult to generate an electric field inclined with respect to the electrode surface uniformly in the entirety of pixel regions. As a result, the liquid crystal molecules respond to the application of the voltage in a delayed manner in a part of the pixel regions, which results in an image sticking phenomenon.
The structure disclosed in Japanese Laid-Open Publication No. 8-341590 requires a projections to be formed of a resist or the like on a base plate. This increases the number of production steps and thus raises costs.
According to one aspect of the invention, a liquid crystal display device includes a first substrate; a second substrate; and a liquid crystal layer interposed between the first substrate and the second substrate and having liquid crystal molecules therein. The first substrate includes a first electrode facing the liquid crystal layer. The second substrate includes a second electrode facing the liquid crystal layer. The first electrode, the second electrode, and a region of the liquid crystal layer supplied with a voltage by the first electrode and the second electrode define a pixel region which is a unit for display. The pixel region includes a plurality of sub pixel regions, in each of which the liquid crystal molecules are aligned in an axial symmetrical manner. At least one of the first electrode and the second electrode includes a plurality of openings, which are regularly arranged, in the pixel region. The at least one of the first electrode and the second electrode having the openings include a plurality of polygonal sub electrode regions, each of which has at least a part of the plurality of openings at least one of at corners and along and overlapping sides thereof. The plurality of sub pixel electrodes are defined by the sub electrode regions.
In one embodiment of the invention, the first electrode includes a plurality of pixel electrodes arranged in a matrix, and the plurality of pixel electrodes are each connected to a scanning line and a signal line through a switching device. The second electrode is a counter electrode facing the plurality of pixel electrodes. The plurality of pixel electrodes each have at least one of the plurality of sub electrode regions.
In one embodiment of the invention, at least two of the plurality of sub electrode regions are congruent polygons to each other and share a common side.
In one embodiment of the invention, the polygons each have rotationary symmetry, and the liquid crystal molecules are aligned in an axially symmetrical manner with respect to an axis for the rotationary symmetry of the polygons.
In one embodiment of the invention, at least two of the plurality of sub electrode regions are polygons sharing a common side, and the openings are at least 2 xcexcm away from an edge of the pixel electrode.
In one embodiment of the invention, the polygons are congruent to each other.
In one embodiment of the invention, the polygons each have rotationary symmetry, and the liquid crystal molecules are aligned in an axially symmetrical manner with respect to an axis for the rotationary symmetry of the polygons.
In one embodiment of the invention, the liquid crystal layer is formed of a liquid crystal material having a negative dielectric anisotropy, and the liquid crystal molecules of the liquid crystal material are aligned substantially vertically with respect to surfaces of the first substrate and the second substrate in the state where no voltage is applied.
In one embodiment of the invention, at least one of the first substrate and the second substrate includes a column-like projection, for controlling the thickness of the liquid crystal layer, outside the pixel region.
In one embodiment of the invention, the liquid crystal layer includes a chiral dopant, and the liquid crystal molecules have a spiral pitch which is about four times the thickness of the liquid crystal layer.
In one embodiment of the invention, the liquid crystal display device further includes a pair of polarizers interposing the first substrate and the second substrate, and at least one monoaxial phase plate having a negative refractive index anisotropy.
In one embodiment of the invention, the liquid crystal display device further includes a pair of polarizers interposing the first substrate and the second substrate, and at least one monoaxial phase plate having a positive refractive index anisotropy.
In one embodiment of the invention, the liquid crystal display device further includes a pair of polarizers interposing the first substrate and the second substrate, and at least one biaxial phase plate at least one of between the first substrate and the polarizer closer to the first substrate than to the second substrate and between the second substrate and the polarizer closer to the second substrate than to the first substrate.
In one embodiment of the invention, at least two of the plurality of sub electrode regions are polygons sharing a common side, and at least one of sides of at least one of the sub electrode regions matches at least one of edges of the pixel electrode.
In one embodiment of the invention, the polygons are congruent to each other.
In one embodiment of the invention, the polygons each have rotationary symmetry, and the liquid crystal molecules are aligned in an axially symmetrical manner with respect to an axis for the rotationary symmetry of the polygons.
In one embodiment of the invention, the liquid crystal layer is formed of a liquid crystal material having a negative dielectric anisotropy, and the liquid crystal molecules of the liquid crystal material are aligned substantially vertically with respect to surfaces of the first substrate and the second substrate in the state where no voltage is applied.
In one embodiment of the invention, at least one of the first substrate and the second substrate includes a column-like projection, for controlling the thickness of the liquid crystal layer, outside the pixel region.
In one embodiment of the invention, the liquid crystal layer includes a chiral dopant, and the liquid crystal molecules have a spiral pitch which is about four times the thickness of the liquid crystal layer.
In one embodiment of the invention, the liquid crystal display device further includes a pair of polarizers interposing the first substrate and the second substrate, and at least one monoaxial phase plate having a negative refractive index anisotropy at least one of between the first substrate and the polarizer closer to the first substrate than to the second substrate and between the second substrate and the polarizer closer to the second substrate than to the first substrate.
In one embodiment of the invention, the liquid crystal display device further includes a pair of polarizers interposing the first substrate and the second substrate, and at least one monoaxial phase plate having a positive refractive index anisotropy at least one of between the first substrate and the polarizer closer to the first substrate than to the second substrate and between the second substrate and the polarizer closer to the second substrate than to the first substrate.
In one embodiment of the invention, the liquid crystal display device further includes a pair of polarizers interposing the first substrate and the second substrate, and at least one biaxial phase plate at least one of between the first substrate and the polarizer closer to the first substrate than to the second substrate and between the second substrate and the polarizer closer to the second substrate than to the first substrate.
In one embodiment of the invention, at least one of the first substrate and the second substrate has an alignment fixing layer, for controlling the axial symmetrical alignment of the liquid crystal molecules, between the liquid crystal layer and at least one of the first electrode and the second electrode.
In one embodiment of the invention, the first electrode includes a plurality of pixel electrodes arranged in a matrix, and the plurality of pixel electrodes are each connected to a scanning line and a signal line through a switching device. The second electrode is a counter electrode facing the plurality of pixel electrodes. The plurality of pixel electrodes each have at least one of the plurality of sub electrode regions.
In one embodiment of the invention, at least two of the plurality of sub electrode regions are congruent polygons to each other and share a common side.
In one embodiment of the invention, the polygons each have rotationary symmetry, and the liquid crystal molecules are aligned in an axially symmetrical manner with respect to an axis for the rotationary symmetry of the polygons.
In one embodiment of the invention, at least one of the first substrate and the second substrate includes a column-like projection, for controlling the thickness of the liquid crystal layer, outside the pixel region.
In one embodiment of the invention, the liquid crystal layer is formed of a liquid crystal material having a negative dielectric anisotropy, and the liquid crystal molecules of the liquid crystal material are aligned substantially vertically with respect to surfaces of the first substrate and the second substrate in the state where no voltage is applied.
In one embodiment of the invention, the liquid crystal display device further includes a pair of polarizers interposing the first substrate and the second substrate, and at least one monoaxial phase plate having a negative refractive index anisotropy.
In one embodiment of the invention, the liquid crystal display device further includes a pair of polarizers interposing the first substrate and the second substrate, and at least one monoaxial phase plate having a positive refractive index anisotropy.
In one embodiment of the invention, the liquid crystal display device further includes a pair of polarizers interposing the first substrate and the second substrate, and at least one biaxial phase plate at least one of between the first substrate and the polarizer closer to the first substrate than to the second substrate and between the second substrate and the polarizer closer to the second substrate than to the first substrate.
In one embodiment of the invention, the liquid crystal layer includes a chiral dopant, and the liquid crystal molecules have a spiral pitch which is about four times the thickness of the liquid crystal layer.
In one embodiment of the invention, at least one of the first electrode and the second electrode has a plurality of recessed portions which are regularly arranged.
In one embodiment of the invention, at least one of the first substrate and the second substrate includes a column-like projection, for controlling the thickness of the liquid crystal layer.
In one embodiment of the invention, the liquid crystal layer is formed of a liquid crystal material having a negative dielectric anisotropy, and the liquid crystal molecules of the liquid crystal material are aligned substantially vertically with respect to surfaces of the first substrate and the second substrate in the state where no voltage is applied.
In one embodiment of the invention, the liquid crystal display device further includes a pair of polarizers interposing the first substrate and the second substrate, and at least one monoaxial phase plate having a negative refractive index anisotropy at least one of between the first substrate and the polarizer closer to the first substrate than to the second substrate and between the second substrate and the polarizer closer to the second substrate than to the first substrate.
In one embodiment of the invention, the liquid crystal display device further includes a pair of polarizers interposing the first substrate and the second substrate, and at least one monoaxial phase plate having a positive refractive index anisotropy at least one of between the first substrate and the polarizer closer to the first substrate than to the second substrate and between the second substrate and the polarizer closer to the second substrate than to the first substrate.
In one embodiment of the invention, the liquid crystal display device further includes a pair of polarizers interposing the first substrate and the second substrate, and at least one biaxial phase plate at least one of between the first substrate and the polarizer closer to the first substrate than to the second substrate and between the second substrate and the polarizer closer to the second substrate than to the first substrate.
In one embodiment of the invention, the liquid crystal layer includes a chiral dopant, and the liquid crystal molecules have a spiral pitch which is about four times the thickness of the liquid crystal layer.
According to another aspect of the invention, a method for producing a liquid crystal display device including a first substrate, a second substrate, and a liquid crystal layer interposed between the first substrate and the second substrate and formed of a liquid crystal material having liquid crystal molecules, wherein the first substrate includes a first electrode facing the liquid crystal layer; the second substrate includes a second electrode facing the liquid crystal layer; the first electrode, the second electrode, and a region of the liquid crystal layer supplied with a voltage by the first electrode and the second electrode define a pixel region which is a unit for display; and the pixel region includes a plurality of sub pixel regions, in each of which the liquid crystal molecules are aligned in an axial symmetrical manner includes the steps of forming a plurality of openings regularly arranged in at least one of the first electrode and the second electrode in the pixel region, so that the at least one of the first electrode and the second electrode having the openings include a plurality of polygonal sub electrode regions, each of which has a part of the openings at least at one of corners and along and overlapping sides thereof; injecting a mixture of a photocurable resin and the liquid crystal material into a gap between the first substrate and the second substrate; and irradiating the mixture with light while supplying the mixture with a voltage, thereby curing the photocurable resin and thus forming an alignment fixing layer.
In an LCD device according to the present invention, an electrode for applying a voltage to the liquid crystal layer has an opening (an area which does not act as an electrode) in a pixel region, which is a unit for display. Since no electric field is generated at the opening, an electric field around the opening is inclined with respect to a direction normal to the surface of the electrode. For example, liquid crystal molecules having a negative dielectric anisotropy are aligned so that longitudinal axes thereof are vertical to the electric field. Accordingly, the liquid crystal molecules are aligned in a radial (i.e., axially symmetrical) manner around the opening due to the oblique electric field. As a result, the dependency of the display quality of the LCD device on the viewing angle, which is caused by the refractive index anisotropy of the liquid crystal molecules, is averaged in all azimuth directions.
In an embodiment where polygonal sub electrode regions having openings at least either at corners or along and overlapping sides thereof, the liquid crystal molecules are aligned in an axially symmetrical manner in a plurality of sub pixel regions in each of the pixel regions. In an embodiment where the polygonal sub electrode regions are congruent to each other, the sub pixel regions defined by the polygonal sub electrode regions are arranged highly symmetrically. Accordingly, the uniformity of the viewing angle characteristic is improved. In an embodiment where the polygons each have rotationary symmetry (n-fold symmetry), the viewing characteristic is further improved.
In an embodiment where the electrode has a recessed portion in a pixel region, the liquid crystal molecules above the recessed portion are aligned vertically with respect to an area of the vertical alignment layer, the area being concaved in conformity of the recessed portion. In other words, the liquid crystal molecules above the recessed portion are tilted in an axially symmetrical manner with respect to the center axis of the recessed portion. In an embodiment where the recessed portion is at an intermediate position between two adjacent openings, the axis for the axial symmetrical alignment matches the center axis of the recessed portion. Thus, the position of the center axis for the axial symmetrical alignment is secured and stabilized.
In an embodiment where the openings are at least 2 xcexcm away from the edge of the pixel electrode, the alignment of the liquid crystal molecules is prevented from becoming unstable due to the lateral electric field generated by scanning lines and signal lines (bus lines) provided for connecting the active devices in the vicinity of an edge of the pixel electrode.
In an embodiment where at least one side of at least one sub electrode region matches at least one edge of the pixel electrode, generation of disclination at the edge of the pixel electrode is suppressed.
In an embodiment where an alignment fixing layer is provided between the liquid crystal layer and at least either the first substrate or the second substrate, the alignment of the liquid crystal molecules is stabilized, which provides a bright display.
Thus, the invention described herein makes possible the advantages of providing an LCD device having a satisfactory viewing angle characteristic and generating no image sticking phenomenon, and a method for producing the same.
These and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.